Pop off (turbo bypass )valve

I wanted to know.....The "pop off" valves that Indy and F1 cars use...are they
pretty much the same thing that Audi uses? Why is it that only Audi uses this
design which is better (and quieter..ever hear a wastegate flap rattle?) What
are the symptoms of it going on it's way out? Any noises or
sounds?.....Thanks.....Steve
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